The Internet is upon us. Millions of people access the Internet each day to download information stored on remote computers about everything from their health to their wealth. As anyone who has ever used the Internet knows (hereafter these people will be referred to as xe2x80x9cusersxe2x80x9d), it sometimes takes a while for information to be transmitted from such remote computers to a user""s computer. In the case of video or image information, the wait can be very long. Much of the wait is due to the fact that information is still sent using relatively slow speeds, e.g. less than 56K bits /sec. Reacting to consumer and business demands for faster transmission of information, techniques have been developed to transmit information at higher speeds or more efficiently. One such method which has been developed uses DSL signals and equipment instead of standard telephone signals and equipment. Together the signals and equipment comprise a DSL xe2x80x9cline.xe2x80x9d Many telephone companies now offer DSL lines to businesses and consumers who are interested in avoiding the xe2x80x9cwaiting gamexe2x80x9d described above.
A common way to transmit and receive information over a DSL line is to use DMT signals. A transceiver which is designed to transmit and receive DMT signals is referred to as a DMT transceiver.
A DSL line can be thought of as a xe2x80x9ccommunication channelxe2x80x9d through which information is transmitted, received, re-transmitted and re-received. In order for one DMT transceiver to correctly extract and reconstruct a signal sent from another DMT transceiver, it is important for the receiving transceiver to know as much as possible about the communication channel through which the signal has passed. One parameter which is often used by DMT transceivers to characterize a communication channel is referred to as the xe2x80x9cimpulse responsexe2x80x9d of a channel.
For the most part, there are two ways to measure the impulse response of a communication channel; using a reference signal or using a xe2x80x9cblind channelxe2x80x9d estimation method. The first technique requires the transmission of a separate xe2x80x9ctrainingxe2x80x9d or reference signal between each transceiver. This reference signal is used to determine the impulse response of the channel of interest. One example of a reference signal is a signal which comprises a pseudorandom sequence of digital bits. Once the impulse response of a given channel is estimated it can be used by one DMT transceiver to reconstruct signals originally transmitted by another DMT transceiver. Generally, the impulse response of a given communication channel can be determined faster (i.e., in less time) using a reference signal than using a blind channel estimation method. The drawback of the reference signal method, however, is that it requires the generation and use of a separate reference signal. A DMT transceiver which determines impulse response using a reference signal is usually more expensive than one that uses a blind channel estimation method. In addition, there exists circumstances where it is impractical to use a separate reference signal regardless of cost. In still other instances, the transmission, reception and re-transmission of a reference signal may become impaired due to the failure of a return path channel.
Given the drawbacks and circumstances just described, manufacturers would like to incorporate blind channel estimation methods into their DMT transceivers. Up until now, existing blind channel estimation methods have been expensive to implement as well. Much of this expense is due to the fact that existing estimation methods require the solution of a set of linear, simultaneous equations. These equations involve complex mathematical operations such as division, square-rooting and matrix inversion. To complete these types of operations, complex and expensive hardwaresoftware is required. In contrast, the hardware/software commonly used in existing DMT transceivers (e.g., fixed point arithmetic circuitry) is relatively inexpensive and not capable of completing such operations. Understandably, manufacturers have been reluctant to incorporate the type of hardware/software required to complete such complex operations into their DMT transceivers in order to avoid the associated higher costs which come along with such a choice.
It is believed that simplifying the type of operations used to complete blind channel estimates of the channel impulse response of a communication channel for a DMT signal will lead to lower cost DMT transceivers.
Accordingly, it is desirable to provide methods and devices for simplifying the type of operations used to complete blind channel estimates of the channel impulse response for a DMT signal.
In accordance with the present invention there are provided methods and devices for completing blind channel estimates of the channel impulse response for a DMT signal. Novel devices comprise an arithmetic unit adapted to estimate the impulse response using an autocorrelation function of a received signal. Other devices/arithmetic units make use of the autocorrelation function to further simplify the estimation of the impulse response. The impulse response of both static and time-varying channels can be determined using devices envisioned by the present invention. Optionally, each of these devices may comprise a receiving unit adapted to receive a DMT signal and a memory unit adapted to store at least the autocorrelation function. Some examples of such a device are a DMT modem, a DSL modem, a digital signal processor or digital signal processor chip set. The device may also be realized as fixed point arithmetic circuitry.
In addition to devices, the present invention also envisions programmable mediums, such as floppy disks, optical disks and other memory devices for storing program code written in a form known in the art and methods for carrying out the features and functions of the present invention.
The present invention and its advantages can be best understood with reference to the drawings, detailed description of the invention and claims that follow.